It is worth mentioning that, with the exception of universal equipment, AC motors can be considered as machines that obtain constant speeds. In this way, it is possible to present stator coils of an induction motor connected, so that it is feasible to double the number of poles, reducing the speed in half. The stators present can be composed of two independent windings vf2s-112m , calculated for the specific number of poles that are expected, by means of reversible poles, to vary the poles, and with a small number of connections, the synchronous speed of the motor can vary.
That is to say, each of these windings can be connected in a way that allows two different speeds, in the ratio of two by one, thus obtaining up to four synchronous speeds independently, therefore, will never be able to provide speeds at the intermediate level. With winding rotor induction motors it is possible to obtain any speed from zero to approximately the synchronism speed, by varying a simple resistance attached to the winding of the rotor, and which does not imply heating of the rotor, since losses resistance are external to the motor.